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9097 



Bureau of Mines Information Circular/1986 



Bureau of Mines Research Into Reducing 
Materials-Handling Injuries 

By Richard L linger and Thomas G. Bobick 



UNITED STATES DEPARTMENT OF THE INTERIOR 






, ^ 



Information Circular 9097 

n / 



Bureau of Mines Research Into Reducing 
Materials-Handling Injuries 

By Richard L Linger and Thomas G. Bobick 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 




Library of Congress Cataloging in Publication Data: 






c6 



V 7 



n 



7 



Unger, Richard L 

Bureau of Mines research into reducing materials-handling injuries. 

(Information circular; 9097) 

Bibliography: p. 22. 

Supt. of Docs, no.: I 28.27:9097. 

1. Mine haulage - Safety measures. 2. Mine haulage- Accidents. 3. Coal mines and min- 
ing-Safety measures. 4. Coal mines and mining- Accidents. 5. Spine -Wounds and injuries. 
I. Bobick, T. G. II. United States. Bureau of Mines. III. Title. IV. Series: Information cir- 
cular (United States. Bureau of Mines); 9097. 

TN295.U4 [TN331] 622 s [622'.8] 86-600129 



CONTENTS 

Page 

Abstract 1 

Introduct ion 2 

Acknowledgments 2 

Past research to reduce underground materials-handling injuries 3 

Program 1 3 

Program 2 3 

Program 3 4 

Present areas of cooperation 5 

Present research project 5 

General description of the supply-handling system 6 

Organization problems 6 

Storage areas 6 

Supply packaging 7 

Excessive manual materials handling 7 

Lack of mechanical assists 8 

Other hazards 8 

Accident analysis 8 

Proposed solutions 8 

Systems approach — unitized-load supply system 9 

Unitizing supply loads 12 

Modular packaging 13 

Job redesign 13 

Mechanical-assist devices 13 

Task or load redesign 14 

Task elimination 17 

Laboratory simulation 18 

Summary 21 

References 22 

ILLUSTRATIONS 

1. Materials-handling flowcharts 7 

2. Scoop-mounted forks and adapter plate 10 

3. Forks attached to low-seam scoop 11 

4. Experimental underground supply-handling forklift 11 

5. Summary flowcharts of materials paths using palletization 12 

6. Prototype mine jack and wheel changer during testing 14 

7. Pivot boom mounted on maintenance vehicle 15 

8. Scoop beam at an eastern Kentucky coal mine 15 

9. Acceptable levels of lifting, vertical reference planes 16 

10. Acceptable levels of lifting, transverse reference planes 17 

11. Hanging miner cable: laboratory simulation 18 

12. Building a stopping: laboratory simulation 19 

13. Handling rock dust: laboratory simulation 19 

14. Controlled studies related to lifting in the stooped posture 21 



11 



TABLES 



Page 



1. Materials handling and back injuries for an eastern Kentucky coal company, 

1983 9 

2. Accident frequency and average cost for nonfatal accidents reported to 

MSHA, 1983 9 

3. Energy expenditure requirements for performing specific simulated low-coal 

mining activities 20 

4. Energy expenditure and grades of work 20 







UNIT OF MEASURE ABBREVIATIONS USED IN THIS 


REPORT 


ft 




foot L/min 


liter per minute 


h 




hour lb 


pound 


in 




inch min 


minute 


kca 


1/min 


kilocalorie per minute pet 


percent 


kg 




kilogram yr 


year 



BUREAU OF MINES RESEARCH 
INTO REDUCING MATERIALS-HANDLING INJURIES 



By Richard L. linger 1 and Thomas G. Bobick 2 



ABSTRACT 

The Bureau of Mines entered into a cooperative agreement with an east- 
ern Kentucky coal mining company to comprehensively redesign the flow of 
equipment and supplies throughout its underground mines. Items were 
tracked from delivery to the warehouse and from surface storage areas to 
their final usage locations underground. Three underground mines were 
visited, and a great variety of tasks were videotaped for subsequent 
laboratory analysis. Of particular interest were tasks that required 
manual handling of the supplies or equipment components. Activities 
such as handling daily supplies (concrete blocks, rock dust, and cross- 
beams) and handling or lifting the continuous miner power cable were de- 
termined to be the most hazardous. 

Recommendations to the company included redesigned surface storage 
areas to facilitate the use of forklift vehicles to load the underground 
supply cars. Designs were also developed for different mechanical- 
assist devices to help in unloading the supply cars underground and 
to handle equipment maintenance tasks underground. Additionally, the 
videotapes of the underground manual handling tasks became the basis for 
simulating those activities in controlled laboratory conditions. This 
testing will contribute to developing guidelines for proper lifting 
techniques for low-seam coal mines. 



'Civil engineer. 
^Mining engineer. 
Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA, 



INTRODUCTION 



Underground coal mining has justifiably 
developed a reputation for being an ex- 
tremely hazardous occupation. The condi- 
tions encountered in the underground 
environment (possibility for fires, ex- 
plosions, and roof falls) pose a high 
potential for fatalities and injuries. 
Extensive research by the Bureau of Mines 
and the coal mining industry, together 
with enforcement of Federal regulations, 
has substantially reduced the catastroph- 
ic disasters associated with mine explo- 
sions and fires that were commonly en- 
countered in the earlier years of this 
century. During the 1930' s and 1940' s, 
more than 1,000 miners were killed yearly 
in underground coal mines (JO . •* Injuries 
and deaths now typically occur as single 
incidents, and the number of fatalities 
each year currently ranges from 100 to 
150. 

As mining technology has improved and 
work conditions have become somewhat 
safer, the major disasters have de- 
creased. The problems that remain are 
the kinds of accidents and injuries that 
occur in any industrial setting, although 
they may well happen more frequently in 
mining. Specifically, back injuries con- 
stitute the largest single category of 
lost-time accidents in the mining in- 
dustry. The mining environment, by its 
very nature, presents extremely difficult 



working conditions not normally encoun- 
tered in general industry. Lack of ade- 
quate illumination and uneven footing 
contribute to tripping hazards; wet con- 
ditions can cause slippage accidents; and 
low seam height forces the miners to work 
on their knees or in a stooped, bent-over 
posture. All of these hazards contribute 
to the back injury problem. 

The Mine Safety and Health Administra- 
tion (MSHA) Health and Safety Analysis 
Center, located in Denver, CO, indicated 
that in 1978-79 approximately 34 pet of 
the accidents that occurred while han- 
dling materials in underground coal mines 
resulted in back injuries (2^). In 1981, 
approximately 25 pet of the more than 
37,000 accidents in the mining industries 
involved the back ( _3_) . Additionally, 
back injuries account for more lost work- 
days than any other type of injury; for 
example, 40 pet of the lost-time back 
injuries incurred by underground coal 
miners during 1981 resulted in the em- 
ployee's missing more than 4 weeks of 
work (_3) . 

Statistics compiled by MSHA for 15 
mines in the central Pennsylvania area 
indicated that, during the years 1981 
to 1984, accidents related to manual han- 
dling of supplies and materials ranged 
from 28 to 50 pet of all the accidents in 
those mines. 



ACKNOWLEDGMENTS 



The authors want to extend their sin- 
cere appreciation to the following em- 
ployees of the Bureau's Pittsburgh Re- 
search Center: William Doyak and George 
Fischer, mechanical engineering techni- 
cians, for fabricating the mechanical- 
assist devices and delivering them to the 
test mines for field evaluation; Sean 
Gallagher, research physiologist, for 
assisting with the simulation studies at 
the University of Kentucky and for his 

^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this report. 



input to the writing of the "Laboratory 
Simulation" section of this report; and 
Henry Kellner, industrial engineering 
technician, for his suggestions and modi- 
fications to the underground task analy- 
sis procedure, for designing and con- 
structing the low-seam mine simulator, 
and for his assistance in conducting the 
simulation studies at the University of 
Kentucky. 

Additionally, the authors want to thank 
the management and workers of the eastern 
Kentucky coal company that cooperated 
with this research program. 



PAST RESEARCH TO REDUCE UNDERGROUND MATERIALS-HANDLING INJURIES 



During the mid-1970' s, the Bureau began 
to research the possibility of developing 
a systems approach to mechanical handling 
of the daily supplies and equipment used 
in the underground environment in order 
to reduce the number of accidents and in- 
juries from manual handling activities. 
The three research programs discussed be- 
low included design of hardware intended 
to reduce such accidents and injuries. 

PROGRAM 1 

The first program resulted in a de- 
tailed study (4) that defined the physi- 
cal characteristics of the supplies that 
are manually handled, the typical envi- 
ronmental conditions under which the sup- 
plies are handled (including distances 
moved) , injury data associated with the 
manual handling tasks, and an estimate of 
the daily supply-maintenance-production 
tasks that had the best possibilities for 
replacement by mechanical handling de- 
vices. This study defined, in great de- 
tail, the supply flow in typical under- 
ground mines and identified the items 
that were (and still are) handled under- 
ground, including the range of sizes and 
weights. 

This work resulted in classifying the 
supply-handling functions of the various 
items used underground into five general 
categories: 

1. Production end use . — The handling 
of items during their end use at the 
working face, such as rock dusting, roof 
bolting, and erecting temporary ventila- 
tion curtains (this activity represented 
11.2 pet of the total accidents studied 
in this 22-mine research project). 

2. Production supply . — The handling of 
materials from the surface storage areas 
to locations near the working face (but 
excluding the actual end use handling) , 
such as transportation of the rock dust, 
roof bolts, support timbers, or ven- 
tilation curtains (49.5 pet of the 
accidents) . 

3. Section move . — The handling of ma- 
terials as mining proceeds from one 



production section to another, such as 
moving haulage belts, tearing up or re- 
laying rails, or moving airlines, com- 
pressors, or longwall face supports (13.0 
pet of the accidents) . 

4. Equipment maintenance . — The han- 
dling of items involving the maintenance 
of mine equipment, such as removing mo- 
tors from face equipment, replenishing 
hydraulic oil or transmission fluid, or 
replacing extinguisher canisters (16.3 
pet of the accidents). 

5. Mine maintenance . — The handling of 
supplies for maintenance of the mine it- 
self, such as erecting permanent venti- 
lation stoppings, setting crossbars and 
cribbings for roof support, and install- 
ing or upgrading of rail (10.0 pet of the 
accidents) . 

These designations were utilized by sub- 
sequent researchers (_5 - _7) • 

Essentially, this early study provided 
valuable information on the materials- 
handling practices in underground mining. 
This program identified the importance 
of mechanical-assist devices for manual 
lifting-lowering-maneuvering tasks, based 
on the injury frequencies for the equip- 
ment maintenance and mine maintenance 
handling modes. Although the program was 
very thorough, logical, and well planned, 
the prototype vehicle developed (a three- 
wheeled, battery-powered vehicle, with a 
6-degrees-of-f reedom manipulator) was far 
too complex for easy maintenance and us- 
age in underground coal mines. 

PROGRAM 2 

The second program (_5_) followed di- 
rectly from the first one and made use 
of the extensive materials-handling data 
generated by the previous research. The 
objective of this second project was to 
design, construct, implement, and eval- 
uate a system for the mechanical han- 
dling of production supplies in under- 
ground coal mines; the end result was a 
battery-powered, skid-steer forklift that 
was equipped with ancillary handling 
attachments. 



The report contains an excellent de- 
scription of the current supply-handling 
methods, various materials-handling vehi- 
cles commercially available to the mining 
industry, and the supply-handling prob- 
lems that are the most hazardous, have 
high labor costs, or interrupt produc- 
tion. The study identified the need for 
mechanization of the loading-unloading 
tasks at the working section. Research- 
ers also looked at the typical supply- 
handling systems in underground coal 
mines and investigated the possibilities 
of unitizing (palletizing) the supply 
loads. Additionally, specifications of 
a mechanical handling system that could 
handle palletized loads were discussed 
and design concepts for such a system 
generated. Finally, researchers evalu- 
ated the potential and cost effectiveness 
of the concepts, selected the most appro- 
priate concept to develop a workable de- 
sign, and then constructed the prototype 
piece of equipment. 

The prototype vehicle was a battery- 
powered forklift, which was permissible 
for use in underground coal mines; it was 
fairly successful in its initial testing. 
A few design deficiencies were identi- 
fied, which are being improved upon in a 
second-generation, diesel-powered fork- 
lift now being designed and tested by the 
Bureau in-house. The permissible fork- 
lift method of handling palletized daily 
supplies in underground coal mines has 
great potential for reducing manual han- 
dling of materials. The results should 
be a reduction in materials-handling in- 
juries and more efficient of supplies, as 
well as savings in daily supply-handling 
labor. 

PROGRAM 3 

Data from the two earlier studies indi- 
cated that production supply, mine main- 
tenance, and equipment maintenance ac- 
count for approximately 76 pet of all 
materials-handling accidents. The third 
research program (6^) was initiated in 
1981 to investigate and design equipment 
to reduce the manual effort (and hence 
the accidents and injuries) associated 
with mine and equipment maintenance 



activities. This program began with a 
literature review with the manual mate- 
rials-handling problem, which indicated 
that except for the Bureau-funded re- 
search, no maintenance-related programs 
for the mining industry had been con- 
ducted. A number of mines were then vis- 
ited to observe maintenance activities 
and to discuss the problems with the 
miners and safety personnel. The two 
prior Bureau research programs (4-5) were 
used to identify the items handled dur- 
ing all types of supply activities. Ac- 
cident data were analyzed to identify 
possible trends and any hazardous tasks 
that could be addressed during this spe- 
cific project. 

Thus, specifications were compiled to 
help devise a mine-equipment maintenance 
vehicle. A series of vehicle concepts 
was developed by the contractor. Howev- 
er, because of the resultant complexity 
and high cost of the proposed machines, 
the contractor was requested to devise a 
series of materials-handling devices or 
tools (instead of a vehicle) that could 
be fabricated by a typical mine mainte- 
nance shop. Based on the accident sta- 
tistics, the personnel interviews, and 
the mine visits, eight device-tool con- 
cepts were developed (_8) . Of these, the 
three most useful devices were fabricated 
and provided to an eastern Kentucky coal 
company for evaluation and testing. The 
three devices, which have been undergoing 
testing since early in 1984, are de- 
scribed in the section "Job Redesign." 

In late 1983, the coal company cooper- 
ating in the testing of the materials- 
handling devices developed an outline of 
the Preventive Back Injury Program to re- 
duce back injuries for its employees. 
Specific program goals were a reduction 
of injuries by 80 pet within an 18-month 
period after implementation. The preven- 
tive program included a discussion of 
workplace modification and job redesign, 
and a training program that emphasized 
proper lifting techniques and the impor- 
tance of exercise and correct diet. This 
proposed program became the basis for 
further cooperation between the mining 
company and the Bureau. 



PRESENT AREAS OF COOPERATION 



Two categories mentioned in the Cooper- 
ator' s Preventive Back Injury Program — 
lifting techniques and workplace modi- 
fication and/or job redesign — are areas 
where the Bureau is presently doing re- 
search and where in-mine cooperation be- 
gins. During discussions regarding the 
in-mine testing of the materials-handling 
devices, the cooperating company inquired 
whether the Bureau could assist in devel- 
oping its comprehensive program for pre- 
venting back injuries. The Bureau agreed 
to help in this venture, since it was re- 
lated to on-going Bureau research that 
included a detailed analysis of the man- 
ual handling activities in underground 
coal mines and their relationship to back 
injuries for certain work groups. The 
cooperator agreed to allow the Bureau to 
gather data at its mines and to use vol- 
unteers for laboratory simulations of 
certain materials-handling tasks. 

The cooperator runs three low-seam 
mines (defined as having seam thicknesses 
less than 48 in). Compared with working 
in high-seam (greater than 72 in) under- 
ground operations, working in low coal 
prevents the miners from standing erect, 
thus forcing them to perform heavy work 
while in stooped or kneeling positions. 
This imposes significantly more stress on 
their backs than experienced by other in- 
dustrial workers, who can lift supplies 
and move about in an erect posture. 

The traditional approach to reducing 
back injuries has been to train the 
miners to be more aware of the restric- 
tions caused by the existing environmen- 
tal conditions. Although regular train- 
ing is important, ideally the task should 
be redesigned or modified to reduce the 
potential of injury. 

The best way to evaluate a manual han- 
dling task is in terms of the percent- 
age of the worker population who can be 



expected to perform the task without 
overexertion or excessive fatigue. The 
higher the percentage of workers who can 
perform the task, the lower the risk of 
injury or illness; the lower the percent- 
age, the higher the risk of injury (9^). 
If a task can be safely performed by only 
a small percentage of workers, it should 
be redesigned or modified so that more 
of the workers can do it. The ideal 
task will fit 90 pet or more of the work 
population. 

When redesign of a heavy lifting task 
is infeasible, workers must be carefully 
selected who can perform that particular 
task safely. The lower the percentage of 
workers who can safely do the task, the 
more carefully the workers should be se- 
lected to avoid an injury ( jO . Detailed 
tables that list the maximum weights ac- 
ceptable to various percentages of the 
male and female industrial population for 
various manual handling tasks, and the 
methodology used to determine these 
weights, are provided in Snook and Cir- 
iello (9) and Snook U0 ) . 

Redesigning the task to fit the average 
worker is the preferred approach, rather 
than trying to select the most suitable 
workers, because it eliminates problems 
that can develop when replacement workers 
have to fill in for absent employees. 

Bureau research studies to be conducted 
with selected coal companies will em- 
phasize the concepts of supply system 
organization and job redesign. In job 
redesign, there will be three primary 
approaches investigated: (1_) utilizing 
mechanical-assist devices, (2) task or 
load redesign, and (3) task elimination. 
Some work has been initiated in all three 
areas, and further plans will be devel- 
oped in the near future. These are dis- 
cussed in more detail in the "Job Rede- 
sign" section of this report. 



PRESENT RESEARCH PROJECT 



Before solutions 
implemented on 
handling problems, 



can be developed and 
specific materials- 
the existing supply 



system has to be thoroughly studied and 
evaluated. A detailed task analysis must 
be conducted to identify problem areas 



that are unique to each particular system 
being investigated. Such a task analysis 
was conducted at three underground mines 
of the cooperating eastern Kentucky coal 
company. 

The techniques used to gather the in- 
formation on manual materials handling at 
these mines involved interviews, on-site 
observations, and accident analysis. All 
facets of the materials-handling system 
were studied, from the purchasing depart- 
ment to the actual end-use handling of 
the supplies. Interviews were conducted 
with purchasing agents, section super- 
visors, warehouse employees, and under- 
ground supply workers to determine how 
they performed their jobs and to document 
any suggestions they had for improving 
the supply distribution system. 

Once the general procedures of the 
supply-handling system were determined, 
the various supplies were traced from 
their arrival at the mine site to their 
final use underground. Videotaping and 
still photography were used to document 
the materials-handling activities. When- 
ever possible, miners and warehouse work- 
ers were interviewed immediately after 
they had completed a task to record their 
impressions of the work and any problems 
they might be having. The videotapes 
were studied to uncover hazardous manual 
handling tasks and to serve as a basis 
for future work in futher task analyses 
and laboratory simulations. 

GENERAL DESCRIPTION OF THE 
SUPPLY-HANDLING SYSTEM 



taken underground on a pallet and then 
dragged off the flatcar with a chain that 
was attached to a face vehicle (scoop or 
shuttle car). 

Supplies were taken to their end-use 
area by whatever means was convenient. 
Usually they were loaded by hand onto a 
face vehicle, whether the unloading was 
done by hand or mechanically depended on 
the vehicle used. 

In addition, there were no established 
procedures for handling infrequently 
used items such as replacement motors or 
tires. Presumably they were loaded onto 
whatever vehicle was convenient to carry 
them, and all subsequent handling was 
done manually. 

A variety of problems were uncovered in 
the supply-handling systems of the mines 
studied. Most were common to all three 
mines visited. These problems can be 
categorized into two general areas: lack 
of an organized method (systems approach) 
to supply handling, and not using mechan- 
ical-assist devices where feasible. 

ORGANIZATIONAL PROBLEMS 

The problems associated with the lack 
of a systems approach mean that the pre- 
planning and organization vital to run- 
ning an efficient and safe supply-han- 
dling operation are not present. The 
following problems, identified at these 
mines, could be eliminated by utilizing a 
systems approach. 

Storage Areas 



The equipment used to handle supplies 
at mines included battery locomotives and 
tractors, scoops and jeeps, rail-mounted 
and rubber-tired flatcars and trailers, 
and shuttle cars. Generally, supplies 
were loaded by hand onto the supply trip. 
A forklift was available on the surface 
of one mine and used when convenient; 
however, the rough terrain and close con- 
fines of the supply yard usually made its 
use impractical. 

On arriving in the underground sec- 
tion, supplies were generally unloaded 
one piece at a time, by hand. The only 
exception was the roof plates, which were 



Both the surface and underground stor- 
age areas were, to some extent, unorga- 
nized and mismanaged. Supplies were not 
always placed where they could be loaded 
or unloaded most efficiently. For exam- 
ple, the concrete blocks used to con- 
struct ventilation stoppings were stacked 
where a forklift could not conveniently 
reach them; the supply workers frequently 
had to handle them twice before they were 
loaded onto the supplly car for the 
trip underground. Many of the smaller 
items, such as wedges and cap blocks, 
were piled randomly, with little apparent 
concern for breakage or loss. This lack 



of organization can easily contribute to 
strain and sprain injuries by causing 
supplies to be handled many times. 

Supply Packaging 

Many times supplies were packaged in 
such a way as to magnify the problems of 
handling once they were underground. 
Roof bolts are a good example. During 
this study, roof bolts were delivered in 
wire-wrapped bundles of 500 bolts, which 
were loaded onto the supply car by a 
forklift. The wire straps were then cut 
to allow the bolts to spread out so they 
could clear a low roof area of the mine 
along the main haulageway. However, this 
meant that the bolts had to be manually 
unloaded underground, three to six at a 
time. What would have been a 1-min task 
using mechanical means (a chain attached 
to the scoop bucket) was turned into a 
20- or 25-min task that involved poten- 
tial pinching, twisting, and lifting haz- 
ards. The Bureau recommendation was to 
contact the vendor to request that the 
bolts be delivered in bundles of 250. 
The smaller bundles could clear the low 
area along the haulageway. Thus, the 
bolts could remain strapped together, 
which would permit workers to use the 
scoop to pull the bundles off the supply 
car to the section storage area, saving 
time and eliminating manual handling. 

Excessive Manual Materials Handling 

This problem is closely related to poor 
materials packaging and storage. Some 
supplies, most notably rock dust bags and 
concrete blocks, were handled as many as 
five times before reaching their end use. 
This means that each block or bag was 
probably lifted and lowered manually four 
or five times before being handled the 
final time to complete the task. This 
unnecessary excessive handling increases 
the risk of strains to the workers and, 
of course, materials breakage. 

Figure 1 shows the flowcharts, devel- 
oped from the task analysis that was 
conducted at each underground mine, of 
the paths that some of the most commonly 
used supplies take through the mine(s). 



ROOF PLATES 




Palletized plates Pallet dragged off 
looded on supply supply cor with chain 
car with forklift 



Loaded manually 
onto face vehicle 



CROSSBEAMS 




KEY 

Q Manual transfer 
O Manual transport 
/\ Mechomcal transfer 



V ) 

n — y use 



Lifted to roof Loaded monually 
"on'" onto face vehicle 
monually 
(end use) 



Unloaded with 
forklift 



ROCK DUST 




Stacked in rear of 
rock dust trailer 



Loaded manually 
onto face vehicle 



CONCRETE BLOCKS 




Transported from 

surface storage 

to supply car 



Looded monually 
onto face vehicle 



FIGURE 1.— Materials-handling flowcharts. 

Three modes of transportation are shown. 
Manual transfer occurs when the materials 
are moved manually with support, such as 
sliding a rock dust bag across a supply 
car. Manual transport refers to unsup- 
ported transportation of materials; an 
example would be carrying a rock dust bag 
to the face area. Mechanical transfer- 
transport covers any handling of sup- 
plies or materials conducted entirely by 
mechanical means. An example of a mech- 
anical transfer would be using a winch to 
drag equipment or supplies to another 
area; an example of a mechanical trans- 
port would be using a forklift to pick up 
and move supplies and equipment. 

The flowcharts show that all supplies 
required some degree of manual handling. 
The supply-handling technique for the 
roof bolt plates, however, eliminated all 
but the most necessary manual handling. 
The other three charts indicate that the 
supplies were being handled unnecessarily 
many times before reaching the end-use 
area. 



LACK OF MECHANICAL ASSISTS 

The following example illustrates the 
problem of not using mechanical-assist 
devices when feasible. On the surface, 
crossbeams were lifted manually onto the 
forklift forks, driven to the supply car, 
and then unloaded manually from the 
forks. These wooden crossbeams, which 
are usually 8 by 8 in or 10 by 10 in, 
with lengths ranging from 10 to 16 ft, 
are installed in haulageways that need 
extensive roof support. They weigh 200 
to 300 lb and were typically lifted and 
supported manually by two workers (and in 
extraordinary cases, a single worker) on 
each end. When the Bureau observed the 
installation of the beams, a hydraulic 
jack that could have assisted in lifting 
the beam was actually moved aside to make 
room for an extra worker to help lift. 

The hazards associated with manual han- 
dling of some of the more common items in 
the mines observed are discussed below: 

1. Crossbeams (timbers) . — Attempting 
to pull heavy timbers to the edge of the 
supply car for unloading is highly haz- 
ardous. Pinched fingers, strains and 
sprains to the trunk and upper and lower 
extremities, and crushed or fractured 
feet are potential injuries. 

2. Posts . — Injuries are similar to 
those for timbers. Back strains occur 
easily from lifting and twisting with the 
posts during installation. 

3. Concrete blocks . — The blocks lo- 
cated in the middle of the supply car 
have to be lifted an extra time and 
placed at the edge of the car for unload- 
ing. Crushing injuries can occur to the 
hands and feet of the supply workers; 
back injuries can occur quite easily be- 
cause of the lifting and twisting move- 
ment during loading and unloading the 
supply car. Additionally, eye injuries 



can occur from pieces of the block chip- 
ping off during loading or unloading. 

4. Rock dust bags . — Loading and un- 
loading 50-lb rock dust bags can cause 
strains or sprains to both the upper and 
lower extremities, as well as to the 
back, from the constant, repetitive 
twisting. Additionally, eye injuries can 
result if the rock dust bag tears and the 
dust gets into the worker's eyes. 

OTHER HAZARDS 

The section floor also presents hazard- 
ous conditions. Blocks and other loose 
materials can lie scattered about. The 
floor is often wet and slippery. Workers 
carrying supplies can trip over the loose 
items or the haulage tracks and can slip 
in the muddy conditions. In addition, 
little is known about the cumulative ef- 
fect that repeated lifting and twisting 
with heavy loads in restricted workspaces 
has on injury rates. The laboratory work 
discussed later in this report begins to 
address this question. 

ACCIDENT ANALYSIS 

The materials-handling accident records 
of the cooperating company for 1983 were 
examined to uncover any trends in acci- 
dent types or parts of the body injured. 
A summary of the materials handling and 
back injuries is given in table 1. 

Given the limited number of accidents, 
little can be said except that, based on 
Bureau experience, the types and causes 
of these materials-handling accidents 
closely parallel those in the coal indus- 
try as a whole. 

A cost analysis was also done on the 
cooperator's accidents reported to MSHA. 
The results of this analysis are given in 
table 2. 



PROPOSED SOLUTIONS 



The following are proposed solutions to 
excessive and hazardous manual materials 
handling in the mines visited: 

1. Implement a systems approach to 
daily supply handling by developing a 
unitized-load supply-handling system for 
each mine. 



2. Develop the concept of job rede- 
sign — this includes developing and uti- 
lizing mechanical materials-handling de- 
vices for some of the more hazardous 
handling tasks, and, where possible, re- 
structuring or eliminating other tasks. 



TABLE 1. - Materials handling and back injuries for 
an eastern Kentucky coal company, 1983 



Activity 



Handling and/or pulling cable.... 

Moving rock , 

Maintenance: 

Tightening or loosening bolts.. 

Changing motor or transmission. 

Other 

Lifting: 

Guard rail on miner , 

Cross ties 

Belt roller , 

Pipe 

Parts 

Hydraulic jack , 

Being struck by or against: 

Back of deck rail , 

Loose coal 

Rerailing mantrip , 

Shoveling 

Unloading rock dust , 

Loading belt structure , 

Welding overhead , 

Washing out dryer , 

Total , 



Number of 
injuries 



Total days 
lost 



1 175 



2 

3 

4 
10 
5 
1 



13 


11 
5 







229 



1 specific accident accounted for a total of 156 days lost. 

TABLE 2. - Accident frequency and average cost for nonfatal accidents 
reported to MSHA, 1983 





Frequency 


Average cost 


Accident type 


United 
States 


Ken- 
tucky 


Coop- 
erator 


United 
States 


Ken- 
tucky 


Coop- 
erator 




8,085 
5,337 
2,748 

1,099 
1,649 


1,077 
698 
379 

178 

201 


28 
18 

10 

5 
5 


$7,312 

5,708 

10,427 

4,421 
14,430 


$8,281 

7,287 

10,111 

4,536 
15,049 


$2,613 




2,824 


Materials-handling: 

Back 


2,233 
3,366 




1,101 



SYSTEMS APPROACH— UNITIZED-LOAD 
SUPPLY SYSTEM 

The general structure of the unitized- 
load or palletized supply-handling system 
is — 

1. On the surface, unit loads or pal- 
lets of supplies will be loaded onto 
low-profile flatcars or trailers by a 
forklift. 



2. Once underground, the loads will be 
handled with some form of a forklift de- 
vice. One possibility that the Bureau is 
testing is a scoop equipped with a spe- 
cial fork attachment. The attachment 
will allow the scoop to switch from the 
bucket to the forks in just a few minutes 
for supply handling and then back to the 
bucket for coal and/or rock clean-up 
(figs. 2-3). A dedicated supply-handling 



10 




FIGURE 2.— Scoop-mounted forks and adapter plate. 



forklift is also an option the Bureau is 
working on for higher seams (fig. 4). 
The supplies will be kept in section 
storage until needed. 

3. As supplies are needed at the face, 
the forklift will be used to transport 
them in unit loads. 

Figure 5 illustrates the paths that 
most supplies would take if this system 
were implemented. The Bureau estimates 
that a unitized-load system could reduce 
manual handling of supplies by up to 60 
pet. 

Implementation of this system would not 
be without problems, some of which are 
described below: 

1. Unit-load handling equipment. — 
There are no fork trucks commercially 
available that are permissible for under- 
ground coal mines. A proposed cost- 
effective solution is to install forks on 
a proven vehicle to perform the required 
pallet handling. The Bureau is currently 
working on design of a quick-attach fork 



system for low-seam scoops, as mentioned 
previously, as well as a diesel-powered 
permissible fork truck for supply han- 
dling and general mine maintenance. 

2. Unit-load design. — Every inch is 
critical in the thinner seams; most cur- 
rent pallet designs are too high and thus 
not applicable for usage in low-seam 
mines. A pallet would have to be found 
or developed to meet an underground low- 
seam coal mine's height restrictions and 
durability requirements. This is dis- 
cussed further in the next section. 

3. Supply car and trailer design. — To 
minimize the height of the supply trips, 
the supply cars and trailers would have 
to be designed to be as low as possible. 
Several manufacturers have indicated that 
they will build their supply cars to 
whatever specifications are required by 
their customers, which would provide a 
feasible solution to this problem. 

4. Supply vendors. — To have an effec- 
tive supply-handling system, supplies 



11 




FIGURE 3.— Forks attached to low-seam scoop. 




FIGURE 4.— Experimental underground supply-handling forkllft. 



12 



ROOF PLATES 




Pallets loaded on Pallets unloaded 
supply car with at section storage 
(orklift 



Plates loaded manually 
onto face vehicle 




KEY 
O Manual transport 
/^Mechanical transfer 
or transport 



V 



End use 
Pallet taken to face 



CROSSBEAMS 




End 
use 



Picked up 
with forklift 



Unloaded by 

forklift 

onto timber car 



Unloaded with Put into place Taken to end 
forklift by timber car use area with 

in section forklift 



ROCK DUST AND CONCRETE BLOCKS 




Pallets loaded on 

supply car with 

forklift 



Pallets unloaded Taken to end- 
with forklift use area with 

forklift 



FIGURE 5.— Summary flowcharts of materials paths using 
palletization. 



must be delivered to the mine in unit 
loads or stacked so they can be easily 
palletized manually. Most vendors will 
deliver their products however the cus- 
tomer wants them, sometimes at no extra 
cost, but the customer must make a pref- 
erence known. 

5. Supply trip planning. — For the sup- 
ply system to operate most effectively, 
the needs of each underground section 
must be discussed with the supply person- 
nel before the trip is loaded. An accu- 
rate projection of supply needs must be 
made daily with the intent to optimize 
unit-load design, minimize underground 
storage, and minimize the number of sup- 
ply trips. This will allow better inven- 
tory and cost control. 

Unitizing Supply Loads 

The purpose of unitizing supply loads 
is to reduce the handling frequency and 
to facilitate mechanical handling. Gen- 
erally, two types of unit loads are sug- 
gested for underground coal mine sup- 
plies. The first type, end-use units, 
consists of the package that would be de- 
livered to the face or underground end- 
use area. One example of these loads 
would be a pallet or container loaded 
with a small bundle of roof bolts and 
plates, a bag of rock dust, and a small 



bundle of wedges. The second type, stor- 
age units, consists of the larger unit 
loads that would be carried to and stored 
at the section. Examples of this type of 
load are several bundles of roof bolts 
and plates strapped together, a cube 
formed out of bundles of wedges, or sev- 
eral dozen rock dust bags stacked on a 
pallet. The makeup of each type of unit 
should be based on the following 
criteria: 

1. The end-use unit load must not con- 
tain more than the number of pieces used 
in one end-use operation, including an 
allowance for scrap during the operation. 
An end-use operation is the final han- 
dling of the materials. Larger unit 
loads would involve rehandling of loose 
pieces. The number of pieces used in one 
end-use operation depends on the standard 
work practice and equipment in the par- 
ticular mine or section. 

2. The storage unit load must not con- 
tain more than the number of units re- 
quired in the end-use operations for the 
period that the unit load is stored at 
the section. Larger storage unit loads 
would require rehandling of the remaining 
end-use units when the section storage 
area is moved periodically during advance 
or retreat of the section. 

3. Both end-use and storage unit loads 
must be accommodated in the space avail- 
able at the face or the section storage 
area. 

4. The unit loads must be transported 
as individual units on underground trans- 
port vehicles such as the supply car or 
the face trip vehicle. They must be able 
to be unloaded as individual units. 

5. If unit loads are supplied already 
palletized by the supplier, it must be at 
a cost acceptable to the mine operator. 

6. The unit loads, after being pack- 
aged in a container, on a pallet, or in 
a self-wrap, must be within the han- 
dling capacity of the mechanical-handling 
device. 

The final makeup of both types of unit 
loads can be determined only after imple- 
mentation of the supply-handling system. 
Periodic refinements, which will be based 
on input from the mine's suppliers and 
the miners, will be required. 



13 



The choice of suitable pallets or con- 
tainers to carry unit loads will depend 
on the availability of space on the sup- 
ply car, on the section floor conditions, 
and most significantly on whether mate- 
rials arrive on pallets or slipsheets 
from the suppliers. Four basic types of 
pallets that may be needed are — 

1. Timber and post pallets, which have 
removable vertical side bars. 

2. Flat boards for blocks and bags. 

3. Tub pallets for items such as 
grease pails, wedge bundles, etc. 

4. Self-wrapping as a method of pack- 
aging so the unit load can be handled as 
a pallet. 

The flat pallets can be used for stor- 
age and handling at the yard and for some 
unloading at the section. The unit loads 
should be wrapped so they can be mechan- 
ically handled as a single item. This 
way the supply car pallets will be imme- 
diately returned with the empties, avoid- 
ing pallet rehandling at the section. 

In most cases, the width of pallets 
should be limited to a standard 36 in. 
Larger pallets will be too wide to be 
easily unloaded in the narrow space 
available on either side of the supply 
car. However, the exact determination of 
pallet size should be made during the de- 
sign of the supply-handling system. 

An alternative to pallets or contain- 
ers for some loads would be slipsheets. 
Loads such as rock dust would arrive at 
the mine stacked on a strong sheet of 
cardboard or synthetic material that 
would be handled by a specialized fork- 
lift attachment. This would save the 
cost of a pallet and further reduce the 
height of the load. 



face. The empty car can be returned to 
the surface supply yard and replaced by 
another modular car on a single-shift or 
daily basis. Modular packaging, however, 
does have the following limitations: 

1. The unit consisting of sufficient 
rock dust bags, timbers, roof bolts, 
blocks, and the like for a shift or one- 
day operation may be too large to be car- 
ried on one supply car. 

2. The large supply module, if left 
close to the face (in some mine configur- 
ations), could hinder vehicle traffic and 
movement of personnel during the face 
operations. 

3. The supplies required at a section 
will vary during the course of mining. 
Thus, a standard modular package will 
realistically match only the average 
daily needs. Additional nonmodular sup- 
plies would have to be handled daily. 

4. Since so many supplies are stored 
in' a single unit, the pickup of individ- 
ual items may be difficult because of 
overlapping. This mixing may also damage 
some supplies such as rock dust, oil 
cans, and grease pails. 

5. The operations at a section are 
carried out at several locations. For 
example, two rock dust bags may be used 
for dusting the face, while several dozen 
bags may be used for the rock duster or 
the trickle dusters located at crosscuts. 
Similarly, concrete blocks are needed at 
the crosscut that is to be blocked and 
not at the face. The supplies will still 
have to be distributed from the modular 
unit, and rehandling may not necessarily 
be reduced. 

JOB REDESIGN 



Modular Packaging 

Another possible method of unitization 
is based on a modular packaging concept. 
All the supplies needed at the section 
may be bound together in one package and 
supplied to the section as a unit for one 
shift or one day. This method of unit- 
ization can reduce the handling at the 
section. The daily needs of a section 
can be transported on a single supply car 
that can be left close to the working 



There are three primary approaches in 
the concept of job redesign: (1) utiliz- 
ing mechanical-assist devices, (2) task 
or load redesign, and (3) task 
elimination. 

Mechanical-Assist Devices 

Many of the most hazardous manual han- 
dling tasks occur during mine and equip- 
ment maintenance. To address these prob- 
lems, the Bureau has designed specialized 



14 



mechanical-assist devices to handle the 
more difficult jobs. Each device is in- 
expensive and can be built in any reason- 
ably equipped mine shop, which will allow 
the mine to fabricate enough of the de- 
vices to be generally useful. Three of 
the devices developed thus far and their 
intended uses are — 

1. Mine jack-wheel changer. — This de- 
vice (fig. 6) is the underground version 
of the floor jack found in most surface 
maintenance shops. High-flotation tires 
provide quick transport and positioning 
in wet or rocky bottom, and the fore-and- 
aft saddle adjustment permits easy align- 
ment of bolt holes. With a jack of this 
type, a shuttle car tire can be replaced 
or a motor removed from under the machine 
frame without any manual lifting. 

2. Pivot boom. — This device (fig. 7) 
is an adaption of a common device found 



on pickup trucks. It can be used to lift 
and position loads up to 500 lb that are 
adjacent to any machine. 

3. Scoop boom. — This is a hydrauli- 
cally driven boom mounted on the front of 
a scoop for heavy lifting and transport- 
ing (fig. 8). It incorporates a hydrau- 
lic winch and 100 ft of cable for pull- 
ing objects and for general lifting 
activities. 

When the detailed engineering drawings of 
these and other mechanical-assist devices 
are finalized, they will be supplied to 
all interested mining companies. 

Task or Load Redesign 

In this second category, the standard 
rock dust bag may provide an example of 
the advantages of redesigning packaging. 
Rock dust is packaged in heavy paper bags 




FIGURE 6.— Prototype mine jack and wheel changer during testing. 



15 




FIGURE 7.— Pivot boom mounted on maintenance vehicle. 










FIGURE 8.— Scoop boom at an eastern Kentucky coal mine. 



16 



that are fairly unstable and can break 
open rather easily. Although the weight 
of the package, 50 lb, seems reasonable, 
it may be excessive in the unique situa- 
tion of lifting in low-seam mines. 

The unloading of the rock dust supply 
car at the underground storage area was 
observed as part of the task analysis. 
The supply car had a normal load of 216 
rock dust bags. These were unloaded by 
the two supply workers in two 10-min work 
periods separated by a 5- or 10-min rest 
period. Thus each worker unloaded an 
average of 54 bags per 10-min work peri- 
od. Working in low coal, these employees 
generally alternated among working on 
both knees, working on one knee (the oth- 
er one being used as a brace or support) , 
and working in a stooped-over position. 
This task involved fully extending the 
arms and picking up the 50-lb bag (or, if 
possible, sliding the bag across the sup- 
ply car closer to the body and then lift- 
ing it with arms bent) , twisting with the 
load, and then fully extending the arms 
again to place the rock dust bag onto the 
storage pile that is lined up along the 
haulage track. Of course, because of the 
restricted height (42 in) , only about 
eight bags could be stacked on top of one 
another; placing the last two bags on the 
pile involved a great deal of lateral 
twisting and swinging the arms higher 
than the worker's shoulder to put the bag 
at the top of the pile before starting a 
new pile along the track. This slide, 
lift, twist, extend, and place activity 
occurred every 11 seconds for a constant 
10 min before they took a rest. 

Reference 11, "Force Limits in Manual 
Work," gives some idea of the strenuous- 
ness of this particular task. This ref- 
erence was developed in 1980 by the Mate- 
rials Handling Research Unit in the 
Institute of Industrial and Environmental 
Health and Safety of the University of 
Surrey (England) primarily to prevent in- 
juries in the European coal and steel in- 
juries. Figure 9, which is from refer- 
ence 11, presents the acceptable weights 
that can be lifted at various distances 
from the acromion (the prominence) of the 
worker's shoulder; this point is marked 
in the figure by the black dot. 





KEY 

The vertical reference planes 
used in the guide 
/ Hand(s) in front of the trunk 
(sagittal plane) 

2 Hand (s) in a plane at 45° 

3 Hand(s) in line with shoulders 
(coronal plane) 





Age groups 


-40 yr 


4l"50yr 


5l-60yr 




male 


male 


male 


A 


14 kg 


14 kg 


10 kg 


B 


15 kg 


15 kg 


1 1 kg 


C 


20 kg 


20 kg 


14 kg 


D 


22 kg 


22 kg 


16 kg 


E 


25 kg 


25 kg 


18 kg 


F 


28 kg 


28 kg 


20 kg 


G 


30 kg 


30 kg 


2 1 kg 


H 


35 kg 


35 kg 


25 kg 


K 


40 kg 


40 kg 


28 kg 


L 


45 kg 


45 kg 


3 2 kg 


M 


50 kg 


50 kg 


36 kg 



Two-handed upward, vertical forces 
(including lifting) when kneeling on 
one knee with the thigh of the other 
leg approximately parallel to the 
floor. The trunk should be main- 
tained in a reasonably upright 
position, with the weight divided 
equally between the two hands, 
which should be in similar positions 
on either side of the body. 



FIGURE 9.— Acceptable levels of lifting, vertical reference 
planes. (By permission of Butterworth Scientific Ltd., P.O. Box 
63, Westbury House, Bury Street, Guildford, Surrey GU2 5BH, 
UK) 

Assigning acceptable levels of force 
application for a particular activity 
"assumes that the worker [s] can perform 
the particular maneuver in free space, 
and that [they are] not required to carry 
out the activity more than once a minute. 
The effects of space limitation are un- 
known. If the activity has to be per- 
formed more than once per minute, then 
the acceptable levels given in the tables 
should be reduced by 30 pet. . . . Diagram 
1 in each set gives the force levels with 
the hand(s) directly in front of the 
trunk, diagram 2 with the hand(s) in a 
plane at 45° to the left or right, and 
diagram 3 with the hand(s) in a plane in 



17 



line with the shoulders" (11). (Emphasis 
is in the original.) 

Since the workers unloading rock dust 
bags are positioned between the supply 
car (on one side) and the stacks of rock 
dust bags (on the other side) , their 
movements are approximately from a 45° 
plane on the right to a 45° plane on the 
left and then back again. Thus, diagram 
2 in figure 9 is applicable in deter- 
mining what acceptable weight could be 
lifted. Since the workers have to extend 
their arms fully to grasp a rock dust bag 
and then start to lift it, value C or E 
in the table— 20 or 25 kg (44 or 55 lb) — 
would be acceptable for 95 pet of the 
male work force (similar acceptable lim- 
its for female workers have not yet been 
developed). However, since the activity 
is performed more than once per minute, 
the values have to be reduced by 30 pet; 
thus, the acceptable values would really 
be in the range of 14 to 17.5 kg (31 to 
38.5 lb). This is when the workers are 
kneeling; when they are lifting from a 
stooped (standing, but bent over) posi- 
tion, the situation is much more criti- 
cal. The guide (_1J_) "does not consider 
acceptable force levels for workers in 
stooping positions. Stooping is known to 
be dangerous, and should be avoided." 

Figure 10 presents the acceptable lev- 
els of lifting when the hand(s) are in 
the horizontal plane directly in front of 
the body (diagram 2) and when the hand(s) 
are in a plane 45° above (diagram S) and 
45° below (diagram 1) the horizontal 
plane. These positions would correspond 
to the movements of the workers when they 
are placing the rock dust bag at the be- 
ginning of a stack, and at the end (near 
the roof). The critical values, as ex- 
pected, are when the workers have to 
raise the load into the 45° plane above 
the horizontal; these values are again C 
and E— 20 and 25 kg (44 and 55 lb). At 
the same 30-pct reduction factor de- 
scribed previously, the acceptable values 
range from 31 to 38.5 lb. 

As a result of these findings, the Bu- 
reau recommended that the cooperator ini- 
tiate a program to find a supplier who 
will assist in developing a 25- or 30-lb- 
capacity paper tube with a twist-gathered 




2 <■ 




KEY 
The transverse planes used in 
the guide 

2 Hand(s) in the horizontal plane 
level with the shoulders 

3 Hand(s) in a plane 45° above 
the horizontal plane 

/ Hand(s) in a plane 45° below 
the horizontal plone 





Age groups 


= 40 yr 


41-50 yr 


51-60 yr 




male 


male 


male 


A 


14 kg 


14 kg 


10 kg 


B 


15 kg 


15 kg 


1 1 kg 


C 


20 kg 


20 kg 


14 kg 


D 


22 kg 


22 kg 


16 kg 


E 


25 kg 


25 kg 


18 kg 


F 


2 8 kg 


28 kg 


20 kg 


G 


30 kg 


30 kg 


2 1 kg 


H 


35 kg 


35 kg 


25 kg 


K 


40 kg 


40 kg 


28 kg 


L 


45 kg 


45 kg 


32 kg 


M 


50 kg 


50 kg 


36 kg 



Two-handed upward, vertical forces 
(including lifting) when kneeling on 
one knee with the thigh of the other 
leg approximately parallel to the 
floor. The trunk should be main- 
tained in a reasonably upright 
position, with the weight divided 
equally between the two hands, 
which should be in similar positions 
on either side of the body. 



FIGURE 10.— Acceptable levels of lifting, transverse 
reference planes. (By permission of Butterworth Scientific 
Ltd., P.O. Box 63, Westbury House, Bury Street, Guildford, Sur- 
rey GU2 5BH, UK) 



end. The tube would be easier to handle 
because of the lighter weight, and the 
twisted end would provide a more positive 
means of grabbing and handling the pack- 
age. Modifications to other supplies 
may also be considered based on future 
research. 

Task Elimination 

Task elimination is the best way to 
avoid possible injuries, but it presents 
the most difficult change to accomplish. 
One of the most common tasks in under- 
ground coal mining is lifting and secur- 
ing the continuous miner power cable to 
the roof bolt plates so the continuous 
miner and other mobile equipment can 
travel freely without running over and 



18 



damaging the cable. An alternative that 
is being tested is a lightweight cable 
ramp. This device will eliminate the 



hazardous task of lifting the power cable 
by enabling mobile equipment to drive 
safely over the (protected) cable. 



LABORATORY SIMULATION 



A previous Bureau research project (12) 
evaluated the job demands associated with 
working in low-coal mines. The physio- 
logical data were collected as the coal 
miners performed their normal activities 
underground. Ventilation volumes were 
used to estimate the energy requirements 
of the tasks performed. Other, more sen- 
sitive instrumentation that could have 
measured the oxygen consumption could not 
be used since it was not approved for use 
in underground mines. 

In the current study, the Bureau col- 
lected metabolic data while the coopera- 
tor's miners performed several manual 
tasks in a simulated low-seam environ- 
ment. The mine simulator was located in 
a laboratory setting where sophisticated 
instrumentation could be used to collect 
the pertinent data. The objective of the 
laboratory research was to determine how 



closely data from the simulated tasks, 
which were conducted under controlled 
conditions, compared with data collected 
in the underground environemt. 

The initial laboratory simulation test- 
ing was conducted at the University of 
Kentucky during January 1985, using nine 
test subjects regularly employed in un- 
derground coal mines owned by the cooper- 
ator. Each test subject performed four 
specific tasks: lifting the continuous 
miner power cable and securing it to a 
standard roof bolt plate; constructing a 
roof support cribbing and installing 
tightening wedges; lifting and position- 
ing concrete blocks to build a ventila- 
tion stopping; and moving 50-lb rock dust 
bags from one side of the simulator to 
the other. Some of these tasks are shown 
in figures 11 through 13. 




FIGURE 11.— Hanging miner cable: laboratory simulation. 



19 




FIGURE 12.— Building a stopping: laboratory simulation. 




FIGURE 13.— Handling rock dust: laboratory simulation. 



20 



The mine simulator was designed and 
constructed by Bureau employees; it con- 
sisted of standard 2- by 4-in studding 
for the sides, 3/16-in plywood for the 
floor, and chicken wire for the roof. 
The roof design allowed overhead photos 
to be taken is desired, but prevented the 
test subjects from standing upright. The 
roof was variable from 32 to 48 in, in 
increments of 2 in; most tasks were 
conducted with a roof height of 42 in. 
Rock and coal were scattered about on 
the floor, so the test subjects had a 
sense of kneeling in a typical mine 
environment. 

As each task was conducted, high-speed 
films were taken of the subject simulta- 
neously from locations that were perpen- 
dicular to the front and one side of the 
simulator. The analysis of these films 
will determine the range of motion that 
the various body segments of the workers 
moved through as the tasks were con- 
ducted. This type of information, cou- 
pled with anthropometric measurements of 
each miner, will be used to determine the 
amount of torsional loading experienced 
by a miner's lower back during these work 
activities. 

In addition to this biomechanical eval- 
uation, metabolic measurements were col- 
lected for three of the four tasks. 



Metabolic data were not collected for the 
cable lift because this activity occurs 
so quickly that the data would be mean- 
ingless. The other tasks, however, were 
ideal since they were conducted long 
enough so that a measure of the worker's 
energy expenditure (V02> which is the 
volume of oxygen used) was obtainable for 
each activity. Analysis of these data 
will provide an indication of the physio- 
logical cost of the job in terms of the 
volume of oxygen utilized per minute of 
activity performed. Thus, the absolute 
oxygen requirements for the three differ- 
ent tasks will be determined; these data 
will be published in the future. 

Table 3 presents the mean and standard 
deviation of the metabolic data collected 
from the nine test subjects for the three 
simulated tasks. The data indicate that 
building a roof support cribbing and mov- 
ing concrete blocks to build a ventila- 
tion stopping are equally strenuous. 
Moving rock dust bags, however, is quite 
a bit more demanding. Another Bureau- 
funded research study (13) utilized oxy- 
gen-consumption information to catego- 
rize the grade of manual work (table 4). 
Based on these categories, handling 
concrete block and building a cribbing 
are considered heavy work and moving 



TABLE 3. - Energy expenditure requirements for performing 
specific simulated low-coal mining activities 



Task' 



V0 2 , L/min 



Mean Std dev 



Energy, kcal/min 



Mean Std dev 



Building cribbing 

Moving concrete block 

Moving 50-lb rock dust bags, 



1.68 
1.69 
2.06 



0.26 
.32 
.34 



8.4 
8.45 
10.3 



1.3 
1.6 
1.7 



Bureau of Mines-University of Kentucky laboratory simulation 
data. 

*9 replications for each task. 

TABLE 4. - Energy expenditure and grades of work 



Grade of work 


Energy expenditure, kcal 


Approx O2 con- 




Per minute 


Per 8-h shift 


sumption, L/min 




>12.5 

10.5- 12.5 

7.5- 10.0 

5.0- 7.5 

2.5- 5.0 

<2.5 


>6,000 
4,800- 6,000 
3,600- 4,800 
2,400- 3,600 
1,200- 2,400 

<1,200 


>2.5 
2.0- 2.5 




1.5- 2.0 




1.0- 1.5 




.5- 1.0 
<.5 



21 




FIGURE 14.— Controlled studies related to lifting In the stooped posture (while the test subject's expired air is collected and 
analyzed), conducted at the Bureau's Ergonomics Laboratory at the Pittsburgh Research Center. 



rock dust bags is considered very heavy 
work. 

The biomechanical data analysis was 
completed by February 1986. It is impor- 
tant to note that only nine workers have 
been tested under these controlled con- 
ditions; a much larger sample popula- 
tion has to be tested before any meaning- 
ful conclusions can be drawn from this 
testing. 

As a continuation of this research, 
biomechanical and physiological testing 
has been initiated at the Bureau's Pitts- 
burgh Research Center Ergonomics Lab 
(fig. 14). Future plans include conduct- 
ing the same type of underground task 



analysis with selected coal companies in 
central and western Pennsylvania. As the 
task analysis is conducted in the under- 
ground workplace, volunteers will be 
selected from the job categories that 
normally involve a great deal of manual 
handling of supplies and equipment (la- 
borer, supply worker, mechanic, shuttle 
car or scoop operator, continuous miner 
helper, etc.) to participate in labora- 
tory studies under closely controlled 
test conditions. This laboratory testing 
will increase the data base to enable the 
Bureau to develop guidelines for handling 
and lifting supplies and equipment in un- 
derground low-seam coal mines. 



SUMMARY 



Working in underground mines involves 
a great deal of manual handling of mate- 
rials. Accidents from manually han- 
dling supplies and equipment typically 



represent 30 to 40 pet of all lost-time 
accidents in underground coal mining. 

A task analysis conducted at three un- 
derground coal mines in eastern Kentucky 



22 



identified a need for organization in 
both the surface and underground storage 
areas. Additionally, it indicated that 
commercially available materials-handling 
devices should be utilized. Other types 
of mechanical-assist devices were de- 
signed and tested underground in an at- 
tempt to modify several lifting tasks. A 
few tasks were identified that could be 
eliminated by utilizing materials-han- 
dling devices or through modifications to 
the work procedure. 

Another possibility for reducing in- 
juries from manually handling supplies 
depends on communication between the cus- 
tomer and vendor. For example, the ven- 
dor may be able to supply smaller sized 
loads or palletized loads, which can be 
handled more easily at the mine. This 
type of communication is critical. 



The task analysis identified that only 
9 of a total of 48 tasks observed (less 
than 20 pet) were conducted by mechanical 
means; a total of 39 (more than 80 pet) 
were handled manually. The Bureau esti- 
mates that approximately two-thirds of 
the manual handling tasks that were ob- 
served could be modified by existing or 
easily designed mechanical-assist de- 
vices. Finally, the analysis indicated 
that some of the manual activities ex- 
ceeded acceptable lifting limits. 

Laboratory simulation of several lift- 
ing tasks, which tested coal miners under 
controlled conditions, permitted a bio- 
mechanical and physiological analysis of 
those activities. This type of testing 
will be the basis for developing lifting 
guidelines for the underground low-seam 
coal mining industry. 



REFERENCES 



1. National Academy of Sciences. To- 
ward Safer Underground Coal Mines. 1982, 
190 pp. 

2. Mine Safety and Health Administra- 
tion (U.S. Dep. Labor). Back Injuries in 
Coal Mining, 1978-1979. MSHA Yellow- 
jacket, 1980, 10 pp. 

3. Peay, J. M. (comp.). Back Injur- 
ies. Proceedings: Bureau of Mines Tech- 
nology Transfer Symposia, Pittsburgh, PA, 
August 9, 1983, and Reno, NV, August 15, 
1983. BuMines IC 8948, 1983, 110 pp. 

4. Foote, A. L. , and J. S. Schaefer. 
Mine Materials Handling Vehicle (MMHV) 
(contract H0242015, MBAssociates) . Bu- 
Mines OFR 59-80, 1978, 308 pp.; NTIS PB 
80-178890. 

5. Booz Allen and Hamilton Inc. Sys- 
tem for Handling Supplies in Underground 
Coal Mines, Executive Summary. Ongoing 
BuMines contract HO 188049; available upon 
request from R. Unger, BuMines, Pitts- 
burgh, PA. 

6. Canyon Research Group, Inc. /Essex 
Corp. Mine Maintenance Material Handling 
Vehicle: Investigative Study and Concept 
Development. Ongoing BuMines contract 
H0113018; for inf., contact R. Unger, 
BuMines, Pittsburgh, PA. 

7. Unger, R. L. , and D. J. Connelly. 
Materials Handling Methods and Problems 
in Underground Coal Mines. Paper in Back 
Injuries. Proceedings: Bureau of Mines 



Technology Transfer Symposia, Pittsburgh, 
PA, August 9, 1983, and Reno, NV, August 
15, 1983, comp. by J. M. Peay. BuMines 
IC 8948, 1983, pp. 3-13. 

8. Unger, R. L. Mechanization of Ma- 
terials Handling Tasks. Paper in Back 
Injuries. Proceedings: Bureau of Mines 
Technology Transfer Symposia, Pittsburgh, 
PA, August 9, 1983, and Reno, NV, August 

15, 1983, comp. by J. M. Peay. BuMines 
IC 8948, 1983, pp. 102-110. 

9. Snook, S. H., and V. M. Ciriello. 
Maximum Weights and Work Loads Acceptable 
to Female Workers. J. Occup. Med., v. 

16, No. 8, 1974, pp. 527-534. 

10. Snook, S. H. The Design of Manual 
Handling Tasks. Ergonomics J. (London), 
v. 21, No. 12, 1978, pp. 963-985. 

11. Materials Handling Research Unit, 
University of Surrey (England). Force 
Limits in Manual Work. IPC Sci. and 
Technol. Press Ltd., 1980, 25 pp. 

12. Texas Tech University. Mining in 
Low Coal. Volume 1: Biomechanics and 
Work Physiology (contract H0387022) . Bu- 
Mines OFR 162(l)-83, 1981, 175 pp.; NTIS 
PB 83-258160. 

13. . Biomechanical and Work 

Physiology Study in Underground Mining 
Excluding Low Coal (contract J0308058) . 
BuMines OFR 90-85, 1984, 211 pp.; NTIS PB 
85-243566. 



6 U.S. GOVERNMENT PRINTING OFFICE: 1986—605-017/40,071 



INT.-BU.0F MINES,PGH.,PA. 28343 



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Cochrans Mill Road 
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Pittsburgh, Pa. 15236 



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